In recent years, the research on GLP-1 and Exendin 4 has received much attention. Both of them have high homology, so they have good effect on application in Type II diabetes mellitus treatment. GLP-1 is a polypeptide separated and purified from human's intestinal tract, while Exendin 4 is a peptide extracted from venom in Mexican giant lizard. Both GLP-1 and Exendin 4 can promote pancreas to synthesize and secrete insulin in case of low concentration, further help diabetics control their blood glucose. GLP-1 is an intestinal tract incretion secreted by human, generated by proglucagon (Proglucagon) molecule under the action of intestinal tract proteolytic enzyme, and therefore called glucagon polypeptide. In case of the blood glucose level exceeding 6 mmol/L, GLP-1 can promote insulin secretion; while in case of blood glucose level back to normal value, no continuous action occurs, which is very useful to treat Type II diabetes mellitus. There are two kinds of GLP-1 in human body: one is GLP-1(7-36)NH2, which is a polypeptide consisting of 30 aminoacid residues (namely the 7th to 36th aminoacids in proglucagon) with amidated End C; and the other is GLP-1(7-37), which is a polypeptide consisting of 31 aminoacid residues (namely the 7th to 37 the aminoacids in proglucagon). GLP-1(7-36)NH2 and GLP-1(7-37) have the same insulinotropic hormone secretion action. The experiments prove that the interaction of GLP-1 and isolated pancreatic islet cells can promote its insulin secretion in case of the concentration between 1×10−10 and 1×10−11 mol/L, and therefore they are called insulinotropin. U.S. Pat. No. 5,424,286 opens comparative experiments of Exendin 4 and GLP-1 insulinotropic hormone secretion. In comparison with GLP-1, Exendin 4 concentration required for insulin secretion action regeneration is lower, and Exendin 4 has longer half time in human body. The research shows that GLP-1 or Exendin 4 may become a more ideal drug for Type II diabetes mellitus treatment.
An ideal drug for Type II diabetes mellitus treatment reduces fasting blood glucose level and postprandial blood glucose level, does not lead to low blood glucose level, reduces cardiovascular system deuteropathy, and does not other side reaction. GLP-1 is a peptide consisting of 30 aminoacids, and its sequence His-Ala-Glu-Gly-Thr-Phe-Thr-Ser-Asp-Val-Ser-Ser-Tyr-Leu-Glu-Gly-Gln-Ala-Ala-Lys-Glu-Phe-Ile-Ala-Trp-Leu-Val-Lys-Gly-Arg (SEQ ID NO: 1). For diabetes mellitus treatment, this sequence has such advantages as natural sequence generated in human body, many features like the above, and few side reactions. For example, it can inhibit glucogen secretion, slow down stomach intestine evacuation, inhibit appetite for food, etc. In addition, GLP-1 receptor stimulation can also promote cell proliferation and regeneracy to increase insulin secretion and tolerance to sugar. But this sequence has such disadvantage: the first two aminoacids His-Ala are so fast decomposed by dipeptidyl peptidase on human body and deactivated that it has a very short half time only between 90 and 120 seconds in human body, and therefore it is almost useless in clinical treatment. There are a lot of research and patents on GLP-1 sequence reconstruction in China now, but GLP-1 sequence length is not reduced during its sequence reconstruction.
Exendin 4 has a long half time in human body and prominent blood glucose-lowering effect, but chemically synthesized Exendin 4 is a peptide consisting of 39 aminoacids, which has high cost, and as a heterogeny polypeptide, may induce human to generate antibody in case of long-term use, resulting in invalidation